COMPETITIVE ADSORPTION OF BETA-LACTOGLOBULIN AND BETA-CASEIN WITH SPAN-80 AT THE OIL-WATER INTERFACE AND THE EFFECTS ON EMULSION BEHAVIOR

The effect of the oil-soluble emulsifier Span 80 (sorbitan monooleate) on the interfacial properties of the milk proteins beta-lactoglobulin and beta-casein was investigated. The interfacial behaviour was corre lated with the emulsification capacity and orthokinetic stability of o il-in-water (o/w) emulsions. It was found that beta-casein was more se nsitive to the presence of Span 80 than beta-lactoglobulin. The interf acial tension of beta-casein adsorbed layers was affected at lower Spa n 80 concentrations than that of the adsorbed layers stabilised by bet a-lactoglobulin. The emulsification capacity and interfacial concentra tion of beta-casein-stabilised emulsions were also affected at lower c oncentrations of Span 80 than those of emulsions stabilised by beta-la ctoglobulin. This behaviour is likely to be due to the relative surfac e activities of the proteins, and the lower level of surface self-inte raction between the beta-casein molecules. In contrast, the orthokinet ic stability of beta-casein-stabilised emulsions was greater than beta -lactoglobulin-stabilised emulsions in the presence of competing Span 80. This demonstrated that orthokinetic stability is not wholly determ ined by interactions between adsorbed protein molecules.